The Cat 528 Skidder

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Cat 528 Swinger
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1975 Cat Cable Skidder
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Gearmatic 119 winch

The skidder of the day (Cat 528 with ESCO Swinging Grapple) will weigh nearly 40,000 lbs, have 175 horsepower, a grapple on the back, and have 30.5 X 32 tires. The vintage 1975 Cat 528 Cable Skidder is similar in appearance.

If you look at the Wagner specifications of the mid 1950's, you will see that they are essentially the same as the Wagners of 1955, but for the fact that they have proper tires on them. A grapple skidder, of course, is only useful where you can back up to the end of the log, but it saves the operation from having to set a choker on the tree as would be necessary with a machine with a winch on it. The winch line, of course will reach places that a skidder won't go, but then the bigger low pressure tires mean that the skidder will go places that the skidder of 40 years ago wouldn't.. This is all leading up to something, and that something is the Morgan SilvaCom .

The Features

Caterpillar was hardly a market leader in the development of the log skidder. They entered the market in the 1970's after the market well fairly well defined. Their two classic models were the Cat 518 and the larger Cat 528. As of 1996 both model numbers have been discontinued in favor of a slightly newer design. as between the 518 and the 528 the smaller 518 has been vastly more popular probably due to price considerations. The machines are similar in appearance, with thte 518 having a shorter wheel base and a smaller engine and smaller tires. It featured a 'over 100 hp' 4 cylinder engine while the 528 was in the 175 hp class with a 6 cylinder variant of the same engine. The photographs you see here are both of Cat 528's. One with a winch and the other with an aftermarket adaptation of an ESCO 215 swinging grapple.

Although it has not been historically true of Cat, their engineers clearly had visited Oregon before they designed these machines. The 528's you see here have no less than 3 braking systems. First they feature disk brakes on each wheel. These are air over hydraulic activated. The hydraulic circuits and activation for the front wheels and the rear wheels are completely separate with redundant master cylinders and activation units. Additionally, there is a disk brake on the driveshaft behind the transmission which has yet another activation circuit. This circuit features a Bendix-Westinghouse style spring set, air released air can which has a 'panel mounted' push button control. In normal operation, 'stepping on the brakes' operates all three systems (front wheels, back wheels, and drive shaft). Braking is available if anyone of the 3 hydraulic subsystems is functional. On the air side, in the event of a loss of air pressure, the spring lock can on the drive shaft automatically activates stopping the machine. Finally, the push button control serves as a parking brake providing a reasonable expectation that the operator who must leave the machine will be able to find it again in the same location when he/she returns. This is of particular significance to the winch machines as the operators customarily set their own hooks, and the unscheduled departure of the skidder while the operator is setting the chokers can be an unwelcome and dangerous event.

The operator protection features of all machinery, including log skidders has been improving over the years. Long present, though not on the Wagner models, has been a ROPS (Roll over protection system) canopy. The idea is that the operator is suppose to be able to survive an upset of a heavy machine without the operators compartment being squished in case of a roll over. With a log skidder, it is hard to suggest that the feature is inappropriate. Logger skidders can and do overturn on a fairly regular basis. Fortunately, log skidders of today rarely suffer from such an event, and often another machine can come by and upright an upset and the machine can be back in service shortly.

- - Updated 12/31/2012
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